The invention relates to the general field of photoresist processing in the presence of copper, with particular application to the manufacture of write heads for magnetic disk systems.
Referring to FIG. 1, we show, in schematic representation, a cross-sectional view of a write head for a magnetic disk system. The magnetic field needed to perform the write operation is generated by flat coil 16 made up of a number of turns, with 13 being an example of one side of a single turn. Surrounding the flat coil is magnetic material comprising upper and lower pole pieces 12 and 11 respectively. These pole pieces are joined at one end (on the left in this figure) and are separated by small gap 14 at the other end. The magnetic field that is generated by flat coil 16 ends up being concentrated at gap 14. It is sufficiently powerful that the fringing field that extends outwards away from gap 14 is capable of magnetizing the magnetic storage medium over whose surface 15 the head xe2x80x98fliesxe2x80x99. The distance between gap 14 and surface 15 is typically between about 10 and 50 nm.
In the course of manufacturing the various layers that make up the gap region it is often found to be convenient to use copper, either alone or in combination with other materials, in one or more of the layers. As is well known, most or all of these layers will be shaped by means of photolithography. Additionally, a given photolithographic step may not always be implemented exactly as intended, for example misalignment between related structures may have occurred. Under such circumstances it is often possible to strip the unsatisfactory layer of photoresist and repeat the photolithographic step, a process referred to as photo rework.
Certain types of photoresist (notably positive resists) are developed using solutions that are very alkaline, typically having a pH in the range from 10 to about 14. In most cases this poses no problems. However, when one of the afore-mentioned pure or partial copper layers comes into contact with such a high pH solution, it is subject to attack. Thus, when using alkaline developers, any exposed copper must either be kept away from the developer or some way must be found to render the copper immune to attack. The present invention discloses a solution that is based on the second of these alternatives.
No references that describe the exact process of the present invention were uncovered in the course of a routine search of the prior art. Several references of interest were, however, found. For example, U.S. Pat. No. 5,236,552 (Fang) shows a photoresist stripping solution containing a corrosion inhibitor such as BTA. U.S. Pat. No. 5,863,710 (Wakiya et al.) shows a developer solution with an aluminum corrosion inhibitor. U.S. Pat. No. 5,635,339 (Murray) shows a photo-thermographic element using BTA as a co-developer. U.S. Pat. No. 5,316,573 (Brusic et al.) forms a corrosion inhibiting layer by dipping in a solution of copper and BTA. U.S. Pat. No. 5,304,252 (Condra et al.) shows a mask removing process with a corrosion inhibitor of BTA for a printed circuit board.
It has been an object of the present invention to provide a process for developing photoresist in the presence of copper bearing material without corroding the latter.
Another object of the invention has been to be able to perform photo rework in the gap region of the write head of a magnetic disk system without affecting copper bearing surfaces nearby.
These objects have been achieved by protecting all exposed copper bearing surfaces from attack by strongly alkaline solutions of the type used to develop photoresist. Two ways of achieving this are described. In the first method, benzotriazole (BTA) is added to the developing solution which is then used in the normal way, developing time being unaffected by this modification. In the second method, the surface that is to receive the photoresist is first given a dip in a solution of BTA, following which the photoresist is immediately applied and processing, including development, proceeds as normal. For both methods the result is the elimination of all copper corrosion during development.